Electrolyte solution, method for producing electrolyte solution, and electrochemical device

ABSTRACT

There is provided an electrolyte solution including a solvent formed from a sulfone, and a magnesium salt dissolved in the solvent.

BACKGROUND

The present disclosure relates to an electrolyte solution, a method forproducing an electrolyte solution, and an electrochemical device. Morespecifically, the present disclosure relates to a suitable electrolytesolution, and method for producing that electrolyte solution, that isused as the electrolyte layer in a magnesium (Mg) ion battery forexample, and various electrochemical devices having a magnesium ionbattery and the like that uses this electrolyte solution.

Magnesium ion batteries are drawing attention as a next-generationsecondary battery to replace lithium ion batteries due to the fact thatcompared with lithium, magnesium is a much more abundant naturalresource and is far cheaper, the amount of electricity per unit volumethat can be extracted by a redox reaction is large, and there is also ahigh level of safety when used in a battery.

In the past, magnesium electrolyte solutions for a magnesium ion batteryhave all used an ether solvent. Especially, it has been reported thatthe electrolyte solutions that use tetrahydrofuran (THF) have the bestproperties (refer to JP-T-2003-512704, JP-A-2009-21085, and NatureCommunications Volume: 2, Article number: 427 DOI:doi:10.1038/ncomms1435).

However, ether solvents such as THF are difficult to handle due to theirhigh volatility and because they are often toxic. Further, the potentialwindow (the maximum voltage that can be applied without the electrolytesolution degrading) of a magnesium electrolyte solution that uses anether solvent is at most about 3.0 V, which is small. Consequently, ithas not been possible to produce a battery having a high voltage using amagnesium metal negative electrode.

Due to the above reasons, development has proceeded on magnesiumelectrolyte solutions that use a solvent other than THF. As a result, amagnesium electrolyte solution was discovered that can be used onmagnesium alloy (refer to Electrochemistry Communications 16 (2012)103-106).

JP-A-2003-100347 discloses a non-aqueous electrolyte battery that usesalkyl sulfone, which is a non-ether solvent, for the electrolytesolution. Specifically, this non-aqueous electrolyte battery includes apositive electrode, a negative electrode including at least one elementselected from aluminum, calcium, and magnesium, and a non-aqueouselectrolyte solution. This non-aqueous electrolyte solution contains analkyl sulfone represented by R₁R₂SO₂ (wherein R₁ and R₂ represent analkyl group) and at least one selected from an aluminum salt, a calciumsalt, and a magnesium salt in a mixed solvent of the alkyl sulfone andan organic solvent that dissolves the at least one selected from analuminum salt, a calcium salt, and a magnesium salt. As the organicsolvent, at least one selected from γ-butyrolactone, acetonitrile, andpropylene carbonate is used.

SUMMARY

However, in JP-T-2003-512704 there is no description about whether thedisclosed non-aqueous electrolyte solution can be used on magnesiummetal or whether it exhibits an electrochemically reversibleprecipitation/dissolution reaction of magnesium. Therefore, irrespectiveof JP-T-2003-512704, it can be said that the only electrolyte solutionscapable of being used on magnesium metal still use an ether solvent.

Therefore, according to an embodiment of the present disclosure, thereis provided an electrolyte solution, and a method for producing thatelectrolyte solution, that uses a non-ether solvent, can be used onmagnesium metal, and can exhibit an electrochemically reversibleprecipitation/dissolution reaction of magnesium.

According to another embodiment of the present disclosure, there isprovided an electrochemical device having a battery and the like thatuses such an excellent electrolyte solution.

The above-described problems as well as other issues with become clearbased on the following descriptions in the present specification withreference to the attached drawings.

As a result of diligent research to resolve the above problems, thepresent inventors discovered that an electrolyte solution in which amagnesium salt has been dissolved in a solvent formed from a sulfone, oran electrolyte solution in which a magnesium salt has been dissolved ina solvent formed from a sulfone and a non-polar solvent, is effective asan electrolyte solution that can be used on a magnesium metal. Further,the present inventors actually confirmed for magnesium metal that suchan electrolyte solution exhibits a reversible precipitation/dissolutionreaction of magnesium, thereby arriving at the present disclosure. Tothe extent of the present inventors' knowledge, there have been noreports in the past of a magnesium electrolyte solution that uses asulfone solvent which exhibits an electrochemically reversibleprecipitation/dissolution reaction of magnesium.

According to an embodiment of the present disclosure, there is providedan electrolyte solution including a solvent formed from a sulfone, and amagnesium salt dissolved in the solvent.

This electrolyte solution is a magnesium ion-containing non-aqueouselectrolyte solution that contains magnesium ions due to the dissolutionof a magnesium salt in a sulfone. This electrolyte solution typicallycontains a magnesium complex that has a four-coordinate dimer structurein which the sulfone is coordinated to the magnesium.

The sulfone is typically an alkyl sulfone or an alkyl sulfone derivativerepresented by R₁R₂SO₂ (wherein R₁ and R₂ represent an alkyl group).Here, the kind (the number and combination of carbon atoms) of R₁ and R₂is not especially limited, and may be selected as appropriate. Thenumber of carbon atoms of R₁ and R₂ is preferably, although not limitedto, 4 or less. Further, the sum of the number of R₁ carbon atoms and thenumber of R₂ carbon atoms is preferably, although not limited to, 4 ormore to 7 or less. Examples of R₁ and R₂ include a methyl group, anethyl group, an n-propyl group, an i-propyl group, an n-butyl, ani-butyl, an s-butyl group, a t-butyl group and the like. Specificexamples of the alkyl sulfone include at least one selected from thegroup consisting of dimethyl sulfone (DMS), methyl ethyl sulfone (MES),methyl-n-propyl sulfone (MnPS), methyl-i-propyl sulfone (MiPS),methyl-n-butyl sulfone (MnBS), methyl-i-butyl sulfone (MiBS),methyl-s-butyl sulfone (MsBS), methyl-t-butyl sulfone (MtBS), ethylmethyl sulfone (EMS), diethyl sulfone (DES), ethyl-n-propyl sulfone(EnPS), ethyl-i-propyl sulfone (EiPS), ethyl-n-butyl sulfone (EnBS),ethyl-i-butyl sulfone (EiBS), ethyl-s-butyl sulfone (EsBS),ethyl-t-butyl sulfone (EtBS), di-n-propyl sulfone (DnPS), di-i-propylsulfone (DiPS), n-propyl-n-butyl sulfone (nPnBS), n-butyl ethyl sulfone(nBES), i-butyl ethyl sulfone (iBES), s-butyl ethyl sulfone (sBES), anddi-n-butyl sulfone (DnBS). Examples of the alkyl sulfone derivativeinclude ethyl phenyl sulfone (EPhS).

Examples of the magnesium salt include at least one selected from thegroup consisting of magnesium chloride (MgCl₂), magnesium bromide(MgBr₂), magnesium iodide (MgI₂), magnesium perchlorate (Mg(ClO₄)₂),magnesium tetrafluoroborate (Mg(BF₄)₂), magnesium hexafluorophosphate(Mg(PF₆)₂), magnesium hexafluoroarsenate (Mg(AsF₆)₂), magnesiumperfluoroalkyl sulfonate ((Rf1SO₃)₂; MgRf1 is a perfluoroalkyl group),and magnesium perfluoroalkylsulfonyl imidate (Mg((Rf2SO₂)₂N)₂; Rf2 is aperfluoroalkyl group). Among these magnesium salts, MgX₂ (wherein X=Cl,Br, or I) is especially preferred.

The electrolyte solution can optionally contain an additive. Thisadditive is, for example, a salt formed from a cation in which the metalion is at least one atom or group of atoms selected from the groupconsisting of aluminum (Al), beryllium (Be), boron (B), gallium (Ga),indium (In), silicon (Si), tin (Sn), titanium (Ti), chromium (Cr), iron(Fe), cobalt (Co), and lanthanum (La). Alternatively, the additive maybe a salt formed from at least one atom, organic group, or anionselected from the group consisting of hydrogen, an alkyl group, analkenyl group, an aryl group, a benzyl group, an amide group, a fluorideion (F⁻), a chloride ion (Cr⁻), a bromide ion (Br⁻), an iodide ion (I⁻),a perchlorate ion (ClO4⁻), a tetrafluoroborate ion (BF₄ ⁻), ahexafluorophosphate ion (PF₆ ⁻), a hexafluoroarsenate ion (AsF₆ ⁻), aperfluoroalkyl sulfonate ion (Rf1SO₃ ⁻; Rf1 is a perfluoroalkyl group),and a perfluoroalkylsulfonyl imide ion (Rf2SO₂)₂N⁻; Rf2 is aperfluoroalkyl group). By adding such an additive, the ion coinductivityof the electrolyte solution can be improved.

According to an embodiment of the present disclosure, there is provide amethod for producing an electrolyte solution, the method includingdissolving a magnesium salt in a low-boiling-point solvent capable ofdissolving a magnesium salt, dissolving a sulfone in a solution in whichthe magnesium salt is dissolved in the low-boiling-point solvent, andremoving the low-boiling-point solvent from the solution in which thesulfone is dissolved.

As the low-boiling-point solvent capable of dissolving the magnesiumsalt, basically any solvent that can dissolve the magnesium salt and hasa boiling point lower than the selected sulfone can be used. Althoughthis solvent is selected as appropriate, it is preferred to use analcohol. The alcohol may be a monohydric alcohol or a polyhydricalcohol, and may be a saturated alcohol or an unsaturated alcohol.Specific examples of the alcohol include, but are not limited to,methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol,2-butanol (sec-butanol), 2-methyl-1-propanol (isobutanol),2-methyl-2-propanol (tert-butanol), and 1-pentanol.

Further, according to an embodiment of the present disclosure, there isprovided an electrolyte solution including a solvent formed from asulfone and a non-polar solvent, and a magnesium salt dissolved in thesolvent.

The non-polar solvent is to be selected as necessary; however, it ispreferably a non-aqueous solvent having a permittivity and a donornumber that are both 20 or less. Specifically, the non-polar solvent isat least one selected from the group consisting of an aromatichydrocarbon, an ether, a ketone, an ester, and a chain carbonate. Thearomatic hydrocarbon is toluene, benzene, o-xylene, m-xylene, p-xylene,or 1-methyl naphthalene, the ether is diethyl ether or tetrahydrofuran,the ketone is 4-methyl-2-pentanone, the ester is methyl acetate or ethylacetate, and the chain carbonate is dimethyl carbonate, diethylcarbonate, or ethyl methyl carbonate.

The sulfone and the magnesium salt are the same as described above.Further, the same additives as described above may be added to theelectrolyte solution as appropriate.

According to an embodiment of the present disclosure, there is provide amethod for producing an electrolyte solution, the method includingdissolving a magnesium salt in a low-boiling-point solvent capable ofdissolving a magnesium salt, dissolving a sulfone in the solution inwhich the magnesium salt is dissolved in the low-boiling-point solvent,removing the low-boiling-point solvent from the solution in which thesulfone is dissolved, and mixing a non-polar solvent in the solutionfrom which the low-boiling-point solvent was removed.

The sulfone, the magnesium salt, and the low-boiling-point solvent arethe same as described above.

According to an embodiment of the present disclosure, there is providean electrochemical device including an electrolyte solution. Theelectrolyte solution is an electrolyte solution including a solventformed from a sulfone and a magnesium salt dissolved in the solvent, oran electrolyte solution including a solvent formed from a sulfone and anon-polar solvent, and a magnesium salt dissolved in the solvent.

Although the electrochemical device may basically be any device,specific examples include various magnesium-using batteries, capacitors,sensors, magnesium ion filters and the like. Examples of magnesium-usingbatteries include secondary batteries, air batteries, fuel cells and thelike. Secondary batteries are, for example, a magnesium ion battery thathas the above-described electrolyte solution as an electrolyte layer.

Further, according to an embodiment of the present disclosure, there isprovided a battery pack including:

a secondary battery;

a control unit configured to perform controls relating to the secondarybattery; and

a casing configured to enclose the secondary battery,

wherein the secondary battery has an electrolyte solution, and

wherein the electrolyte solution is

an electrolyte solution having a solvent formed from a sulfone and amagnesium salt dissolved in the solvent, or

an electrolyte solution having a solvent formed from a sulfone and anon-polar solvent, and a magnesium salt dissolved in the solvent.

In this battery pack, the control unit controls, for example,charging/discharging, over discharging, or over charging of thesecondary battery.

Further, according to an embodiment of the present disclosure, there isprovided an electronic device configured to receive a supply of powerfrom a secondary battery including an electrolyte solution, wherein theelectrolyte solution is

an electrolyte solution having a solvent formed from a sulfone and amagnesium salt dissolved in the solvent, or

an electrolyte solution having a solvent formed from a sulfone and anon-polar solvent, and a magnesium salt dissolved in the solvent.

Further, according to an embodiment of the present disclosure, there isprovided an electric vehicle including:

a conversion apparatus configured to receive a supply of power from asecondary battery and convert the received power into a vehicle driveforce; and

a control apparatus configured to perform information processingrelating to vehicle control based on information relating to thesecondary battery,

wherein the secondary battery has an electrolyte solution, and

wherein the electrolyte solution is

an electrolyte solution having a solvent formed from a sulfone and amagnesium salt dissolved in the solvent, or

an electrolyte solution having a solvent formed from a sulfone and anon-polar solvent, and a magnesium salt dissolved in the solvent.

In this electric vehicle, the conversion apparatus typically generates adrive force by receiving a supply of power from the secondary batteryand rotating a motor. This motor can utilize regenerative energy.Further, the control apparatus performs information processing relatingto vehicle control based on, for example, the remaining battery level ofthe secondary battery. Examples of the electric vehicle include, inaddition to electric automobiles, electric motorbikes, electricbicycles, railroad wagons and the like, so-called hybrid automobiles.

Further, according to an embodiment of the present disclosure, there isprovided a power system configured to receive a supply of power from asecondary battery and/or supply power from a power source to a secondarybattery,

wherein the secondary battery includes an electrolyte solution, and

wherein the electrolyte solution is

an electrolyte solution having a solvent formed from a sulfone and amagnesium salt dissolved in the solvent, or

an electrolyte solution having a solvent formed from a sulfone and anon-polar solvent, and a magnesium salt dissolved in the solvent.

This power system can be any system, including a simple power apparatus,as long as the system uses electric power. Examples of the power system,which can also store power, include a smart grid, a household energymanagement system (HEMS), vehicles and the like.

Further, according to an embodiment of the present disclosure, there isprovided a power storage power source configured so that an electronicdevice to which power is supplied is connected, the power storage powersource including a secondary battery,

wherein the secondary battery has an electrolyte solution, and

wherein the electrolyte solution is

an electrolyte solution having a solvent formed from a sulfone and amagnesium salt dissolved in the solvent, or

an electrolyte solution having a solvent formed from a sulfone and anon-polar solvent, and a magnesium salt dissolved in the solvent.

The applications of this power storage power source are not limited,basically the power storage power source can be used in any power systemor power apparatus. For example, the power storage power source can beused in a smart grid.

According to the embodiments of the present disclosure described above,an electrolyte solution that uses a sulfone, which is a non-ethersolvent, can be obtained that can be used on magnesium metal andexhibits an electrochemically reversible precipitation/dissolutionreaction. Further, by using this excellent electrolyte solution for anelectrolyte layer, a high-performance electrochemical device having amagnesium ion battery and the like can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 1;

FIG. 2 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 1;

FIG. 3 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 2;

FIG. 4 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 2;

FIG. 5 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 3;

FIG. 6 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 3;

FIG. 7 is a graph illustrating a CV measurement result for examining theoxidation potential at which oxidative degradation of the electrolytesolution of Working Example 1 starts;

FIG. 8 is a line diagram illustrating the ¹H NMR spectra of theelectrolyte solution of Working Example 1;

FIG. 9 is a line diagram illustrating the ¹H NMR spectra of theelectrolyte solutions of Working Examples 1 to 3;

FIG. 10 is a line diagram illustrating the XANES spectra of theelectrolyte solutions of Working Examples 1 to 3;

FIG. 11 is a line diagram illustrating a radial structure function ofthe electrolyte solutions of Working Examples 1 to 3;

FIG. 12 is a graph illustrating a CV measurement result for examiningthe oxidative degradation potential of the electrolyte solution ofWorking Example 1 using three types of working electrode;

FIG. 13 is a line diagram illustrating a MgCl₂-EnPS-toluenethree-dimensional phase diagram;

FIG. 14 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 4;

FIG. 15 is a graph illustrating a CV measurement result of theelectrolyte solution of Working Example 5;

FIG. 16 is a line diagram illustrating a magnesium ion battery accordingto a third embodiment of the present disclosure;

FIG. 17 is an exploded perspective diagram illustrating theconfiguration of the coin battery of Working Example 6;

FIG. 18 is a line diagram illustrating a measurement result of thecharge/discharge properties of the coin battery of Working Example 6;

FIG. 19 is a photograph that shows a scanning electron micrograph of asample of lithium metal that has precipitated on copper using aLiPF₆/EC-DMC electrolyte solution; and

FIG. 20 is a photograph that shows a scanning electron micrograph of asample of magnesium metal that has precipitated on copper using theelectrolyte solution of Working Example 1.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Embodiments for carrying out the present technology (hereinafterreferred to as “embodiments of the present disclosure” will now bedescribed in the following order.

1. First embodiment of the present disclosure (electrolyte solution andproduction method thereof)2. Second embodiment of the present disclosure (electrolyte solution andproduction method thereof)3. Third embodiment of the present disclosure (magnesium ion battery)

1. First Embodiment of the Present Disclosure Electrolyte Solution

The electrolyte solution according to the first embodiment of thepresent disclosure is a magnesium ion-containing non-aqueous electrolytesolution in which a magnesium salt is dissolved in a solvent formed froma sulfone. The sulfone and the magnesium salt may be selected from amongthe examples mentioned above, for example. The molar ratio of thesulfone based on the magnesium salt in the electrolyte solution is, forexample, 4 or more to 35 or less, typically is 6 or more to 16 or less,and preferably is 7 or more to 9 or less. However, the molar range isnot limited to these ranges. The magnesium salt typically includes amagnesium complex that has a four-coordinate dimer structure in whichthe sulfone is coordinated to the magnesium.

(Method of Producing the Electrolyte Solution)

The electrolyte solution can be produced as follows, for example.

First, the magnesium salt is dissolved in an alcohol. As the magnesiumsalt, it is preferred to use an anhydrous magnesium salt. Generally,although magnesium salts do not dissolve in sulfones, they do dissolvewell in alcohols. When the magnesium salt is thus dissolved in thealcohol, the alcohol coordinates to the magnesium. The alcohol may beselected from among the examples mentioned above, for example. As thealcohol, it is preferred to use a dehydrated alcohol. Next, the sulfoneis dissolved in the thus-obtained solution in which the magnesium saltwas dissolved in the alcohol. Then, the alcohol is removed by heatingthis solution under reduced pressure. During this process of removingthe alcohol, the alcohol coordinated to the magnesium is exchanged (orsubstituted) with the sulfone. Based on the above processes, the targetelectrolyte solution is produced.

According to this first embodiment of the present disclosure, amagnesium ion-containing non-aqueous electrolyte solution can beobtained that can be used on magnesium metal and exhibits aprecipitation/dissolution reaction that is electrochemically reversibleat room temperature using a sulfone, which is a non-ether solvent. Thesulfone that is used for the solvent generally has a higher boilingpoint than an ether solvent like THF, and thus has a low volatility andis highly safe. Accordingly, the electrolyte solution can be easilyhandled, which consequently allows the processes when producing amagnesium ion battery, for example, to be greatly simplified. Further,since the electrolyte solution has a wider potential window than pastmagnesium electrolyte solutions that use THF as a solvent, there is awider range of choices for the positive electrode material of themagnesium secondary battery, and the voltage, namely the energy density,of the realizable secondary battery can be improved. In addition, sincethis electrolyte solution has a simple composition, the costs of theelectrolyte solution itself can be substantially reduced.

2. Second Embodiment of the Present Disclosure Electrolyte Solution

The electrolyte solution according to the second embodiment of thepresent disclosure is a magnesium ion-containing non-aqueous electrolytesolution in which a magnesium salt is dissolved in a solvent formed froma sulfone and a non-polar solvent. The sulfone, non-polar solvent, andmagnesium salt may be selected from among the examples mentioned above,for example. The molar ratio of the sulfone based on the magnesium saltin the electrolyte solution is, for example, 4 or more to 20 or less,typically is 6 or more to 16 or less, and preferably is 7 or more to 9or less. However, the molar range is not limited to these ranges. Themagnesium salt typically includes a magnesium complex that has afour-coordinate dimer structure in which the sulfone is coordinated tothe magnesium.

(Method of Producing the Electrolyte Solution)

The electrolyte solution can be produced as follows, for example.

First, the magnesium salt is dissolved in an alcohol. As a result, thealcohol coordinates to the magnesium. As the magnesium salt, it ispreferred to use an anhydrous magnesium salt. The alcohol may beselected from among the examples mentioned above, for example. Next, thesulfone is dissolved in the thus-obtained solution in which themagnesium salt was dissolved in the alcohol. Then, the alcohol isremoved by heating this solution under reduced pressure. During thisprocess of removing the alcohol, the alcohol coordinated to themagnesium is exchanged with the sulfone. After this, the non-polarsolvent is admixed into the solution from which the alcohol was removed.The non-polar solvent may be selected from among the examples mentionedabove, for example. Based on the above processes, the target electrolytesolution is produced.

According to the second embodiment of the present disclosure, the sameadvantages can be obtained as the first embodiment of the presentdisclosure.

Working Example 1

A Mg electrolyte solution (Mg-EnPS) was prepared as follows.

Weighing of the reagents and the mixing operation were carried out in aglove box (Ar/dew point −80 to −90° C.). While stirring 100 mL ofdehydrated methanol (manufactured by Nacalai Tesque, Inc.) with astirrer, 3.81 g of anhydrous magnesium chloride (II) (MgCl₂)(manufactured by Sigma-Aldrich Co., LLC) was added. It was confirmed bymeasuring the external temperature of the reaction vessel with a contactthermometer (T2; manufactured by testo K.K.) that a slight amount ofheat was produced when the MgCl₂ dissolved in the methanol. This heat isgenerated by the heat of reaction when the methanol coordinates to theMg. The Mg in the methanol is thought to have a structure in which themethanol is coordinated to it. Further, there was a slight amount ofwhite cloudiness after the dissolution of the MgCl₂ as well. This isthought to be due to the water present in the methanol reacting with theMg to produce Mg(OH)₂. Since the white cloudiness was slight, synthesiswas continued without filtering.

After dissolution of the MgCl₂, 43.6 g of EnPS was added while stirringwith a stirrer.

The solution was removed from the glove box while maintaining a state inwhich air was prevented from mixing therein. Then, while reducing thepressure using a rotary pump (G-110D, manufactured by ULVACTechnologies, Inc.), the methanol was removed by heating and stirring at120° C. for 2 hours. Although a white sediment was produced when theamount of methanol decreased, the produced sediment dissolved when thepressure reduction and heating were continued. This change in solubilityis thought to be due to the exchange of the Mg ligands from methanol toEnPS. The removal of the methanol was confirmed by ¹H NMR measurement.

Since the white cloudiness produced when the MgCl₂ dissolved in themethanol remained in the sample from which methanol had been removed,the sample was filtered (pore size 0.45 μm, manufactured by WhatmanLtd.) in a glove box.

The prepared electrolyte solution had a Mg:Cl:EnPS ratio of 1:2:8 (molarratio) and a Mg concentration of 0.95 mol/L.

Working Example 2

A Mg electrolyte solution (Mg-EnPS-toluene) was prepared as follows.

Weighing of the reagents and the mixing operation were carried out in aglove box (Ar/dew point −80 to −90° C.). While stirring 11.8 g of theelectrolyte solution of Working Example 1 (Mg-EnPS) with a stirrer, 1.9g of low-moisture toluene (manufactured by Nacalai Tesque, Inc.) wasadded.

The prepared electrolyte solution had a Mg:Cl:EnPS ratio of 1:2:8 (molarratio), a MgCl₂:toluene ratio of 1:2 (molar ratio), and a Mgconcentration of 0.78 mol/L.

Working Example 3

A Mg electrolyte solution (Mg-EnPS-BF₄) was prepared as follows.

Weighing of the reagents and the mixing operation were carried out in aglove box (Ar/dew point −80 to −90° C.). While stirring 11.8 g of theelectrolyte solution of Working Example 1 (Mg-EnPS) with a stirrer, 3.9g of AgBF₄ (manufactured by Tokyo Chemical Industry Co., Ltd.) (ratio ofMgCl₂:AgBF₄ in the electrolyte solution of 1:2 (molar ratio)) was added.It was confirmed by measuring the external temperature of the reactionvessel with a contact thermometer (T2; manufactured by testo K.K.) thatheat was produced when the AgBF₄ was added. The AgBF₄ was added at arate at which the temperature of the sample did not exceed 40° C. due tothis generation of heat. This heat is generated by the heat of reactionwhen AgCl is formed. The produced AgCl precipitates. After adding all ofthe AgBF₄ and then stirring for 1 day with a stirrer, the AgCl wasremoved by filtering (pore size 0.45 μm, manufactured by Whatman Ltd.)with a centrifugal separator (Chibitan II, manufactured by MilliporeCorporation) (maximum RCF 5,200×g (51,000 m/s²), 10 min)

The prepared electrolyte solution had a Mg:EnPS ratio of 1:8 (molarratio), a Mg:BF₄ ratio of 1:2 (molar ratio), and a Mg concentration of0.95 mol/L.

(Electrolyte Solution Cyclic Voltammetry (CV) Measurement)

To examine the electrical properties of the thus-prepared electrolytesolutions of Working Examples 1 to 3, the cyclic voltammetry (CV) of theelectrolyte solutions was measured. The measurement was carried out atroom temperature using a three electrode cell (amount of electrolytesolution 1 mL), using a platinum (Pt) electrode (diameter 1.6 mm,manufactured by BAS) for the working electrode and a magnesium (Mg) wire(diameter 1.6 mm, manufactured by Nilaco Corporation) for the counterelectrode and the reference electrode (Ar/dew point −80 to −90° C.).

Measurement of the first cycle was carried out by, starting from an opencircuit state (OCV), changing the voltage in order of OCV→about −1.5V→about +2.0 V so that at first the potential of the working electrodewith respect to the reference electrode was decreased by about 1.5 V tothe reduction side, then increased by about 2.0 V to the oxidation side,and finally returned to the OCV. The rate at which the potential wasapplied was set at 5 mV.

FIGS. 1 and 2 are graphs illustrating the CV measurement results of theelectrolyte solution of Working Example 1 (Mg-EnPS). The horizontal axisin FIGS. 1 and 2 represents the potential of the working electrodeversus the potential of the reference electrode. From these graphs itcan be seen that an electrolyte solution capable of reversiblydissolving and precipitating Mg can be prepared based on a compositionof only MgCl₂ and EnPS. From FIG. 2 it can be seen that the larger thecycle number, the greater the current that flows during oxidation andreduction. This is thought to be due to the state of the electrodesurface changing. Further, after CV measurement, a black deposit waspresent on the working electrode and at the lower portion of the workingelectrode. This is the Mg produced by reduction. The reason why theamount of current on the oxidation side is smaller than the amount ofcurrent on the reduction side is thought to be due to Mg produced byreduction peeling from the electrode surface.

FIGS. 3 and 4 are graphs illustrating the CV measurement results of theelectrolyte solution of Working Example 2 (Mg-EnPS-toluene). It can alsobe seen from these graphs that an electrolyte solution capable ofreversibly dissolving and precipitating Mg can be prepared based on acomposition of MgCl₂, EnPS, and toluene. From a comparison with FIGS. 1and 2, it can be seen that the potential at which oxidation andreduction of Mg starts hardly changes even if toluene is added. Thissuggests that the structure of the Mg complexes relating to oxidationand reduction is similar. However, when toluene is added, despite thefact that the viscosity of the electrolyte solution decreases, thecurrent flowing during oxidation and reduction decreases in both cases.This suggests that adding toluene causes a change in the dissociationstate of the electrolyte solution ions. It is noted that a tendency forthe current flowing during oxidation and reduction to increase as thecycle number increases like that seen with the electrolyte solution ofWorking Example 1 (Mg-EnPS) was not seen in FIG. 4. In FIG. 4, a randomcurrent value was seen for each cycle.

FIGS. 5 and 6 are graphs illustrating the CV measurement results of theelectrolyte solution of Working Example 3 (Mg-EnPS-BF₄). From thesegraphs it can be seen that the electrolyte solution of Working Example 3exhibits a different waveform to the CV measurement results for theelectrolyte solution of Working Example 1 (Mg-EnPS) and the electrolytesolution of Working Example 2 (Mg-EnPS-toluene), thus indicating that aplurality of redox reactions are occurring. This suggests that thestructure of the Mg complexes relating to oxidation and reduction in theelectrolyte solution of Working Example 3 is different to that of theelectrolyte solutions of Examples 1 and 2. Further, considering thatonly the electrolyte solution of Working Example 3 does not includechlorine, it is highly likely that chlorine plays an important role inthe oxidation and reduction behavior confirmed in Working Examples 1 and2. The remaining Ag used during preparation also has an effect.

FIG. 7 is a graph illustrating a CV measurement result for examining theoxidation potential at which oxidative degradation of the electrolytesolution of Working Example 1 (Mg-EnPS) starts. The rate at which thepotential was applied was set at 10 mV. As can be seen from FIG. 7, withthe electrolyte solution of Working Example 1 (Mg-EnPS), oxidativedegradation occurred when the potential of the working electrode wasgreater than the potential of the reference electrode by 3.5 V or more.

(¹H NMR Measurement)

The ¹H NMR of the intermediate preparation product of the electrolytesolutions of Working Examples 1 to 3 and of the electrolyte solutions ofWorking Examples 1 to 3 was measured to examine the coordination of EnPSto magnesium. The ¹H NMR measurement was carried out using the NOVA 400(400 MHz) manufactured by Varian, Inc. Since the environment of theelectrolyte changes if a deuterated solvent is added, the electrolytesolution was measured as a crude solution in situ. Consequently, themeasurement was carried out without locking with a deuterated solvent,and the chemical shift was corrected using a separately measuredexternal reference. Deuterated chloroform was used as the externalreference. The peak position of the included chloroform that did notturn into a deuterated solvent was 7.26 ppm. A measurement sample wasproduced by sealing about 0.6 mL in a 5 mm-diameter NMR tube in a glovebox (Ar/dew point −80 to −90° C.).

FIG. 8 illustrates the ¹H NMR measurement result of the electrolytesolution of Working Example 1 (Mg-EnPS) along with the results for EnPSand for comparison the prepared EnPS-MeOH and Mg-EnPS-MeOH, for thepurpose of observing ligand exchange during electrolyte solutionpreparation. The EnPS-MeOH was a sample in which EnPS and methanol weremixed in the same ratio as during preparation of the electrolytesolution of Working Example 1 (Mg-EnPS), and the Mg-EnPS-MeOH was asample in which EnPS was added after MgCl₂ was dissolved in methanol inthe same ratio as during preparation of the electrolyte solution ofWorking Example 1 (Mg-EnPS). All of the spectra were normalized on boththe vertical axis and the horizontal axis based on the peak of thenormal propyl end moiety (a in the chemical formula of EnPS illustratedin FIG. 8) in the EnPS that is considered to be the least susceptible tothe influence of the coordination to Mg among the EnPS signals.

In FIG. 8, a comparison of the EnPS-MeOH spectra and the spectra of thesample obtained by adding MgCl₂ to EnPS-MeOH (Mg-EnPS-MeOH) shows thatthe peak for the methyl group moiety (f on the methanol illustrated inFIG. 8) on the Mg-EnPS-MeOH methanol has shifted to a lower field, andthat the peak for the hydroxyl group moiety (g on the methanolillustrated in FIG. 8) on the Mg-EnPS-MeOH methanol has broadened. Thissuggests that the methanol is coordinated to the Mg by the OH moiety.Further, since the peak for the hydrogens (c and d in the chemicalformula of EnPS illustrated in FIG. 8) closet to the EnPS oxygen hasshifted to a slightly lower field, it can also be thought that the EnPSis also coordinated. In addition, since only one of these peaks isobserved, it is also thought that the methanol and EnPS underwent ligandexchange at a faster rate than the observation time of the of the NMR.

Next, a comparison of the Mg-EnPS-MeOH spectra and the spectra of asample obtained by removing the methanol from Mg-EnPS-MeOH (Mg-EnPS)shows that the peak for the hydrogens (c and d in the chemical formulaof EnPS illustrated in FIG. 8) closet to the Mg-EnPS oxygen has shiftedto a lower field. This suggests that by removing the methanol, there ismore EnPS than magnesium, and that the EnPS is more stronglycoordinated.

Based on the above, when MgCl₂ is dissolved in methanol, the methanol orCl is coordinated to the magnesium, and by adding EnPS the methanol, theEnPS, and the Cl are coordinated. By removing the methanol from themixture, the EnPS and the Cl are coordinated to the magnesium.

FIG. 9 illustrates the ¹H NMR measurement results of the electrolytesolution of Working Example 1 (Mg-EnPS), the electrolyte solution ofWorking Example 2 (Mg-EnPS-toluene), and the electrolyte solution ofWorking Example 3 (Mg-EnPS-BF₄) along with the results for EnPS and forcomparison the prepared EnPS-toluene, for the purpose of observing theeffects of toluene dilution of the electrolyte solution of WorkingExample 1 (Mg-EnPS) and chlorine removal with AgBF₄. The EnPS-toluenewas a sample in which EnPS and toluene were mixed in the same ratio asduring preparation of the electrolyte solution of Working Example 2(Mg-EnPS-toluene). All of the spectra were normalized on both thevertical axis and the horizontal axis based on the peak of the normalpropyl end moiety (a in the chemical formula of EnPS illustrated in FIG.9) in the EnPS that is considered to be the least susceptible to theinfluence of the coordination to Mg among the EnPS signals.

In FIG. 9, a comparison of the EnPS spectra and the EnPS-toluene spectrashows that the peak for the hydrogens (c and d in the chemical formulaof EnPS illustrated in FIG. 9) closet to the EnPS oxygen of theEnPS-toluene has shifted to a higher field. From this it can be seenthat by adding toluene the state of the EnPS changes. In view of this,when the Mg-EnPS and the Mg-EnPS-toluene spectra are compared, since thepeak for the hydrogens (c and d in the chemical formula of EnPSillustrated in FIG. 9) closet to the EnPS oxygen of the Mg-EnPS-toluenehas shifted to a slightly higher field, there is the possibility thatsome kind of change has also occurred in the bond with the magnesium dueto the addition of the toluene.

Further, a comparison of the Mg-EnPS and the Mg-EnPS-BF₄ spectra showsthat the Mg-EnPS-BF₄ peak has broadened. This can be thought to be dueto the Mg-EnPS-BF₄ having a higher viscosity than the Mg-EnPS.

FIG. 10 illustrates the XAFS (X-ray absorption fine structure)measurement results and the XANES spectra of the electrolyte solution ofWorking Example 1 (Mg-EnPS), the electrolyte solution of Working Example2 (Mg-EnPS-toluene), and the electrolyte solution of Working Example 3(Mg-EnPS-BF₄). Further, FIG. 11 illustrates a radial structure function|F(R)| (wherein R represents the distance from Mg), from which it canclearly be seen than the Mg in the Mg-EnPS and the Mg-EnPS-toluene has afour-coordinate dimer structure, and the Mg-EnPS-BF₄ has asix-coordinated monomer structure. The four-coordinate dimer structureand the six-coordinated monomer structure are as shown below (wherein Lrepresents CL or EnPS).

FIG. 12 illustrates the results of measuring the oxidative degradationpotential of the electrolyte solution of Working Example 1 (Mg-EnPS)using three types of working electrode. The horizontal axis in FIG. 12represents the potential of the working electrode with respect to Mg,and the vertical axis represents the current density. The three types ofworking electrode are stainless steel (SUS 316), platinum (Pt), andnickel (Ni). From FIG. 12, it can be seen that regardless of which ofthe three types of electrode is used, the oxidative degradationpotential (3.6 V) is higher than the oxidative degradation potential(around 2.5 V) of past electrolyte solutions that use an ether solvent.

FIG. 13 illustrates a MgCl₂-EnPS-toluene three-dimensional phasediagram. In FIG. 13, the black circles and the white circles indicatethe composition of the electrolyte solution samples on which theexperiment was performed. The black circles are electrolyte solutionsamples that do not exhibit redox behavior in CV measurement, and thewhite circles are electrolyte solution samples that do exhibit redoxbehavior in CV measurement. It can be seen from these results that thedotted region in FIG. 13 is the region in which redox behavior isexhibited in CV measurement.

Working Example 4

A Mg electrolyte solution (Mg-EiPS) was prepared as follows.

Weighing of the reagents and the mixing operation were carried out in aglove box (Ar/dew point −80 to −90° C.). While stirring 100 mL ofdehydrated methanol (manufactured by Nacalai Tesque, Inc.) with astirrer, 3.81 g of anhydrous magnesium chloride (II) (MgCl₂)(manufactured by Sigma-Aldrich Co., LLC) was added. It was confirmed bymeasuring the external temperature of the reaction vessel with a contactthermometer (T2; manufactured by testo K.K.) that a slight amount ofheat was produced when the MgCl₂ dissolved in the methanol. This heat isgenerated by the heat of reaction when the methanol coordinates to theMg. The Mg in the methanol is thought to have a structure in which themethanol is coordinated to it. Further, there was a slight amount ofwhite cloudiness after the dissolution of the MgCl₂ as well. This isthought to be due to the water present in the methanol reacting with theMg to produce Mg(OH)₂. Since the white cloudiness was slight, synthesiswas continued without filtering.

After dissolution of the MgCl₂, 43.6 g of EiPS was added while stirringwith a stirrer.

The solution was removed from the glove box while maintaining a state inwhich air was prevented from mixing therein. Then, while reducing thepressure using a rotary pump (G-110D, manufactured by ULVACTechnologies, Inc.), the methanol was removed by heating and stirring at110° C. for 2 hours. Although a white sediment was produced when theamount of methanol decreased, the produced sediment dissolved when thepressure reduction and heating were continued. This change in solubilityis thought to be due to the exchange of the Mg ligands from methanol toEiPS. The removal of the methanol was confirmed by ¹H NMR measurement.

Since the white cloudiness produced when the MgCl₂ dissolved in themethanol remained in the sample from which methanol had been removed,the sample was filtered (pore size 0.45 μm, manufactured by WhatmanLtd.) in a glove box.

The prepared electrolyte solution had a Mg:Cl:EiPS ratio of 1:2:8 (molarratio) and a Mg concentration of 1.00 mol/L.

Working Example 5

A Mg electrolyte solution (Mg-DnPS) was prepared as follows.

Weighing of the reagents and the mixing operation were carried out in aglove box (Ar/dew point −80 to −90° C.). While stirring 100 mL ofdehydrated methanol (manufactured by Nacalai Tesque, Inc.) with astirrer, 3.81 g of anhydrous magnesium chloride (II) (MgCl₂)(manufactured by Sigma-Aldrich Co., LLC) was added. It was confirmed bymeasuring the external temperature of the reaction vessel with a contactthermometer (T2; manufactured by testo K.K.) that a slight amount ofheat was produced when the MgCl₂ dissolved in the methanol. This heat isgenerated by the heat of reaction when the methanol coordinates to theMg. The Mg in the methanol is thought to have a structure in which themethanol is coordinated to it. Further, there was a slight amount ofwhite cloudiness after the dissolution of the MgCl₂ as well. This isthought to be due to the water present in the methanol reacting with theMg to produce Mg(OH)₂. Since the white cloudiness was slight, synthesiswas continued without filtering.

After dissolution of the MgCl₂, 48.1 g of DnPS that had been dissolvedin advance using a hot stirrer was added while stirring with a stirrer.

The solution was removed from the glove box while maintaining a state inwhich air was prevented from mixing therein. Then, while reducing thepressure using a rotary pump (G-110D, manufactured by ULVACTechnologies, Inc.), the methanol was removed by heating and stirring at120° C. for 2 hours. Although a white sediment was produced when theamount of methanol decreased, the produced sediment dissolved when thepressure reduction and heating were continued. This change in solubilityis thought to be due to the exchange of the Mg ligands from methanol toDnPS. The removal of the methanol was confirmed by ¹H NMR measurement.

Since the white cloudiness produced when the MgCl₂ dissolved in themethanol remained in the sample from which methanol had been removed,the sample was filtered (pore size 0.45 μm, manufactured by WhatmanLtd.) in a glove box.

The prepared electrolyte solution had a Mg:Cl:DnPS ratio of 1:2:8 (molarratio).

FIGS. 14 and 15 are graphs illustrating the CV measurement results ofthe electrolyte solution of Working Example 4 (Mg-EiPS) and theelectrolyte solution of Working Example 5 (Mg-DnPS), respectively. Fromthese graphs it can be seen that an electrolyte solution capable ofreversibly dissolving and precipitating Mg can be prepared based on acomposition from both the electrolyte solution of Working Example 4(Mg-EiPS) and the electrolyte solution of Working Example 5 (Mg-DnPS).

Third Embodiment of the Present Disclosure Magnesium Ion Battery

Next, a third embodiment of the present disclosure will be described. Inthe third embodiment of the present disclosure, a magnesium ion batterywill be described that uses the electrolyte solution according to thefirst or second embodiment of the present disclosure as an electrolytelayer.

FIG. 16 schematically illustrates the basic configuration of such amagnesium ion battery.

As illustrated in FIG. 16, this magnesium ion battery is configured froma positive electrode 10 and a negative electrode 20 that oppose eachother across an electrolyte layer 30 formed from an electrolytesolution. Examples of positive electrode active materials that can beused for the positive electrode 10 include, but are not limited to,sulfur (S), graphite fluoride ((CF)_(n)), and an oxide or a halide ofvarious metals (e.g., scandium (Sc), titanium (Ti), vanadium (V),chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),copper (Cu), zinc (Zn) etc.). As the negative electrode 20, magnesiummetal alone or a magnesium alloy may be used, for example. Typically,the negative electrode 20 is formed in a sheet shape or a box shape.However, the shape is not limited to these. For example, the negativeelectrode 20 can be formed using a powder. As the electrolyte solutionforming the electrolyte layer 30, the electrolyte solution according tothe first or second embodiment of the present disclosure is used.

(Operation of the Magnesium Ion Battery)

In this magnesium ion battery, during charging, electrical energy isconverted into chemical energy and stored by magnesium ions (Mg²⁺)passing through the electrolyte layer 30 from the positive electrode 10and moving to the negative electrode 20. During discharge, electricalenergy is generated by magnesium ions passing through the electrolytelayer 30 from the negative electrode 20 and returning to the positiveelectrode 10.

Working Example 6

A coin battery was fabricated using magnesium (Mg) for the negativeelectrode, sulfur (S) for the positive electrode, and aMgCl₂/EnPS/toluene electrolyte solution prepared from MgCl₂/EnPS=⅛ (mol)and MgCl₂/toluene=¼ (wt.).

The configuration of this coin battery is illustrated in FIG. 17. Asillustrated in FIG. 17, a gasket 52 was placed on a coin battery can 51.A positive electrode 53 formed from sulfur, a separator 54 made from aglass filter, a negative electrode 55 formed from a 250 μm-thick Mgplate, a spacer 56 formed from a 500 μm-thick stainless steel plate, anda coin battery lid 57 were stacked in that order. Then, the coin batterycan 51 was sealed. The spacer 56 had been spot-welded to the coinbattery lid 57 in advance.

The charge/discharge properties of this coin battery were measured. FIG.18 illustrates those results. It can be seen from FIG. 18 that the cycledeterioration is smaller than the cycle deterioration of pastelectrolyte solutions (refer to Nature Communications Volume: 2, Articlenumber: 427 DOI: doi:10.1038/ncomms1435) that use THF. This is thoughtto be due to differences in the solvent, namely, that sulfur does noteasily dissolve in sulfone (sulfur dissolves in THF).

The elution of sulfur from the positive electrode formed from sulfurinto the electrolyte solution was examined based on measurement of Ramanscattering. The results are shown in Table 1.

TABLE 1 Peak position 473 cm⁻¹ 219 cm⁻¹ 155 cm⁻¹ S S S Sulfur Concen-Concen- Concen- concen- tration tration tration tration (wt %) (wt %)(wt %) (Average) MgCl₂:EnPS = 1:8 0 0 0 0 MgCl₂:EnPS:Toluene = 0 0 0 01:8:4 Mg(AlCl₂ + Et2)-S 1.85 1.80 1.91 1.85 [5] THF - S 1.88 1.69 1.791.79 [7] Toluene - S 1.58 1.79 1.62 1.66 [9]

From Table 1, it can be seen that the solubility of sulfur inMgCl₂:EnPS:toluene=1:8:4 and MgCl₂:EnPS=1:8 was less than the detectionlimit of the Raman scattering measurement. In contrast, about 1.8 to 2wt. % of the sulfur dissolves in 0.25 M Mg(AlCl₂Et₂)/THF.

Since sulfur dissolves in toluene, when a positive electrode made fromsulfur is used, it is desirable that the electrolyte composition has alow toluene content, or that no toluene is included.

Next, the results of investigating the precipitation modes of Mg will bedescribed. FIG. 19 illustrates results obtained by capturing with ascanning electron microscope (SEM) an image of Li metal precipitated ona conducting body (e.g., Cu) on the negative electrode side when aLiPF₆/EC-DMC electrolyte solution is used. FIG. 20 illustrates resultsobtained by capturing with a scanning electron microscope (SEM) an imageof Mg metal precipitated on Cu when a MgCl₂/EnPS electrolyte solution isused. From FIGS. 19 and 20, it can be seen that when Li metal isprecipitated using a LiPF₆/EC-DMC electrolyte solution, dendrites formon the Cu, whereas when Mg metal is precipitated using a MgCl₂/EnPSelectrolyte solution, dendrites do not form on the Cu. Based on this, itcan be said that there is a chance that the problems of a Li metalnegative electrode can be resolved with a Mg metal negative electrode.

According to this third embodiment of the present disclosure, a novelhigh-performance magnesium ion battery can be realized that uses anelectrolyte solution in which a magnesium salt is dissolved in asulfone, or an electrolyte solution in which a magnesium salt isdissolved in a solvent formed from a sulfone and a non-polar solvent.

This magnesium ion battery can be mounted as a drive power source or anauxiliary power source in, for example, a notebook-type personalcomputer, a PDA (a portable information terminal), a mobile phone, acordless phone handset, a video movie recorder, a digital still camera,an e-book, an electronic dictionary, a portable music player, a radio,headphones, a game console, a navigation system, a memory card, acardiac pacemakers, a hearing aid, an electric tool, an electric shaver,a refrigerator, an air conditioner, a television, a stereo, a waterheater, a microwave oven, a dishwasher, a washing machine, a dryer,lighting equipment, toys, medical equipment, a robot, a loadconditioner, traffic lights, a railroad wagon, a golf cart, an electriccart, an electric automobile (including a hybrid automobile), or as apower storage power source for buildings such as homes or powergeneration equipment. Alternatively, this magnesium ion battery can beused for supplying power to such devices. In an electric automobile, theconversion apparatus that converts power into a drive force based on thesupply of power is usually a motor. Examples of the control apparatusfor performing information processing relating to vehicle controlinclude a control apparatus that displays the remaining battery levelbased on information relating to the remaining level of the battery.This magnesium ion battery can also be used as a storage apparatus in aso-called smart grid. This storage apparatus can store power byreceiving a supply of power from another power source. Examples of otherpower sources that can be used include thermal power generation, nuclearpower generation, hydroelectric power generation, solar powergeneration, wind power generation, geothermal power generation, a fuelcell (including a biofuel cell) and the like.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

For example, the numerical values, structures, configurations, shapes,materials and the like mentioned in the above embodiments of the presentdisclosure and the working examples are merely examples which may bechanged as appropriate to different numerical values, structures,configurations, shapes, materials and the like.

Additionally, the present technology may also be configured as below.

(1) An electrolyte solution including:

a solvent formed from a sulfone; and

a magnesium salt dissolved in the solvent.

(2) The electrolyte solution according to (1), wherein the electrolytesolution includes a magnesium complex having a four-coordinate dimerstructure in which the sulfone is coordinated to magnesium.(3) The electrolyte solution according to (1) or (2), wherein thesulfone is an alkyl sulfone or an alkyl sulfone derivative representedby R₁R₂SO₂ (wherein R₁ and R₂ represent an alkyl group).(4) The electrolyte solution according to (3), wherein the alkyl sulfoneis at least one selected from the group consisting of dimethyl sulfone,methyl ethyl sulfone, methyl-n-propyl sulfone, methyl-i-propyl sulfone,methyl-n-butyl sulfone, methyl-i-butyl sulfone, methyl-s-butyl sulfone,methyl-t-butyl sulfone, ethyl methyl sulfone, diethyl sulfone,ethyl-n-propyl sulfone, ethyl-i-propyl sulfone, ethyl-n-butyl sulfone,ethyl-i-butyl sulfone, ethyl-s-butyl sulfone, ethyl-t-butyl sulfone,di-n-propyl sulfone, di-i-propyl sulfone, n-propyl-n-butyl sulfone,n-butyl ethyl sulfone, i-butyl ethyl sulfone, s-butyl ethyl sulfone, anddi-n-butyl sulfone, and the alkyl sulfone derivative is ethyl phenylsulfone.(5) The electrolyte solution according to any one of (1) to (4), whereinthe magnesium salt includes at least one selected from the groupconsisting of magnesium chloride, magnesium bromide, magnesium iodide,magnesium perchlorate, magnesium tetrafluoroborate, magnesiumhexafluorophosphate, magnesium hexafluoroarsenate, magnesium perfluoroalkyl sulfonate, and magnesium perfluoroalkylsulfonyl imidate.(6) The electrolyte solution according to any one of (1) to (5), furtherincluding:

a salt formed from a cation in which a metal ion is at least one atom orgroup of atoms selected from the group consisting of aluminum,beryllium, boron, gallium, indium, silicon, tin, titanium, chromium,iron, cobalt, and lanthanum, or a salt formed from at least one atom,organic group, or anion selected from the group consisting of hydrogen,an alkyl group, an alkenyl group, an aryl group, a benzyl group, anamide group, a fluoride ion, a chloride ion, a bromide ion, an iodideion, a perchlorate ion, a tetrafluoroborate ion, a hexafluorophosphateion, a hexafluoroarsenate ion, a perfluoroalkyl sulfonate ion, and aperfluoroalkylsulfonyl imide ion.

(7) A method for producing an electrolyte solution, the methodincluding:

dissolving a magnesium salt in a low-boiling-point solvent capable ofdissolving a magnesium salt;

dissolving a sulfone in a solution in which the magnesium salt isdissolved in the low-boiling-point solvent; and

removing the low-boiling-point solvent from the solution in which thesulfone is dissolved.

(8) The method for producing an electrolyte solution according to (7),wherein the low-boiling-point solvent is an alcohol.(9) An electrolyte solution including:

a solvent formed from a sulfone and a non-polar solvent; and

a magnesium salt dissolved in the solvent.

(10) The electrolyte solution according to (9), wherein the non-polarsolvent is a non-aqueous solvent having a permittivity and a donornumber that are both 20 or less.(11) The electrolyte solution according to (9) or (10), wherein thenon-polar solvent is at least one selected from the group consisting ofan aromatic hydrocarbon, an ether, a ketone, an ester, and a chaincarbonate ester.(12) The electrolyte solution according to (11), wherein the aromatichydrocarbon is toluene, benzene, o-xylene, m-xylene, p-xylene, or1-methyl naphthalene, the ether is diethyl ether or tetrahydrofuran, theketone is 4-methyl-2-pentanone, the ester is methyl acetate or ethylacetate, and the chain carbonate ester is dimethyl carbonate, diethylcarbonate, or ethyl methyl carbonate.(13) A method for producing an electrolyte solution, the methodincluding:

dissolving a magnesium salt in a low-boiling-point solvent capable ofdissolving a magnesium salt;

dissolving a sulfone in the solution in which the magnesium salt isdissolved in the low-boiling-point solvent;

removing the low-boiling-point solvent from the solution in which thesulfone is dissolved; and

mixing a non-polar solvent in the solution from which thelow-boiling-point solvent was removed.

(14) The method for producing an electrolyte solution according to (13),wherein the low-boiling-point solvent is an alcohol.(15) An electrochemical device including:

an electrolyte solution,

wherein the electrolyte solution is

-   -   an electrolyte solution including a solvent formed from a        sulfone and a magnesium salt dissolved in the solvent, or    -   an electrolyte solution including a solvent formed from a        sulfone and a non-polar solvent, and a magnesium salt dissolved        in the solvent.        (16) The electrochemical device according to (15), wherein the        electrochemical device is a magnesium-using battery, capacitor,        sensor, or magnesium ion filter.        (17) The electrochemical device according to (16), wherein the        battery is a secondary battery, an air battery, or a fuel cell.        (18) The electrochemical device according to (17), wherein the        secondary battery is a magnesium ion battery that has the        electrolyte solution as an electrolyte layer.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2012-216811 filed in theJapan Patent Office on Sep. 28, 2012, the entire content of which ishereby incorporated by reference.

What is claimed is:
 1. An electrolyte solution comprising: a solventformed from a sulfone; and a magnesium salt dissolved in the solvent. 2.The electrolyte solution according to claim 1, wherein the electrolytesolution includes a magnesium complex having a four-coordinate dimerstructure in which the sulfone is coordinated to magnesium.
 3. Theelectrolyte solution according to claim 2, wherein the sulfone is analkyl sulfone or an alkyl sulfone derivative represented by R₁R₂SO₂(wherein R₁ and R₂ represent an alkyl group).
 4. The electrolytesolution according to claim 3, wherein the alkyl sulfone is at least oneselected from the group consisting of dimethyl sulfone, methyl ethylsulfone, methyl-n-propyl sulfone, methyl-i-propyl sulfone,methyl-n-butyl sulfone, methyl-i-butyl sulfone, methyl-s-butyl sulfone,methyl-t-butyl sulfone, ethyl methyl sulfone, diethyl sulfone,ethyl-n-propyl sulfone, ethyl-i-propyl sulfone, ethyl-n-butyl sulfone,ethyl-i-butyl sulfone, ethyl-s-butyl sulfone, ethyl-t-butyl sulfone,di-n-propyl sulfone, di-i-propyl sulfone, n-propyl-n-butyl sulfone,n-butyl ethyl sulfone, i-butyl ethyl sulfone, s-butyl ethyl sulfone, anddi-n-butyl sulfone, and the alkyl sulfone derivative is ethyl phenylsulfone.
 5. The electrolyte solution according to claim 4, wherein themagnesium salt includes at least one selected from the group consistingof magnesium chloride, magnesium bromide, magnesium iodide, magnesiumperchlorate, magnesium tetrafluoroborate, magnesium hexafluorophosphate,magnesium hexafluoroarsenate, magnesium perfluoroalkyl sulfonate, andmagnesium perfluoroalkylsulfonyl imidate.
 6. The electrolyte solutionaccording to claim 5, further comprising: a salt formed from a cation inwhich a metal ion is at least one atom or group of atoms selected fromthe group consisting of aluminum, beryllium, boron, gallium, indium,silicon, tin, titanium, chromium, iron, cobalt, and lanthanum, or a saltformed from at least one atom, organic group, or anion selected from thegroup consisting of hydrogen, an alkyl group, an alkenyl group, an arylgroup, a benzyl group, an amide group, a fluoride ion, a chloride ion, abromide ion, an iodide ion, a perchlorate ion, a tetrafluoroborate ion,a hexafluorophosphate ion, a hexafluoroarsenate ion, a perfluoroalkylsulfonate ion, and a perfluoroalkylsulfonyl imide ion.
 7. A method forproducing an electrolyte solution, the method comprising: dissolving amagnesium salt in a low-boiling-point solvent capable of dissolving amagnesium salt; dissolving a sulfone in a solution in which themagnesium salt is dissolved in the low-boiling-point solvent; andremoving the low-boiling-point solvent from the solution in which thesulfone is dissolved.
 8. The method for producing an electrolytesolution according to claim 7, wherein the low-boiling-point solvent isan alcohol.
 9. An electrolyte solution comprising: a solvent formed froma sulfone and a non-polar solvent; and a magnesium salt dissolved in thesolvent.
 10. The electrolyte solution according to claim 9, wherein thenon-polar solvent is a non-aqueous solvent having a permittivity and adonor number that are both 20 or less.
 11. The electrolyte solutionaccording to claim 10, wherein the non-polar solvent is at least oneselected from the group consisting of an aromatic hydrocarbon, an ether,a ketone, an ester, and a chain carbonate.
 12. The electrolyte solutionaccording to claim 11, wherein the aromatic hydrocarbon is toluene,benzene, o-xylene, m-xylene, p-xylene, or 1-methyl naphthalene, theether is diethyl ether or tetrahydrofuran, the ketone is4-methyl-2-pentanone, the ester is methyl acetate or ethyl acetate, andthe chain carbonate is dimethyl carbonate, diethyl carbonate, or ethylmethyl carbonate.
 13. A method for producing an electrolyte solution,the method comprising: dissolving a magnesium salt in alow-boiling-point solvent capable of dissolving a magnesium salt;dissolving a sulfone in the solution in which the magnesium salt isdissolved in the low-boiling-point solvent; removing thelow-boiling-point solvent from the solution in which the sulfone isdissolved; and mixing a non-polar solvent in the solution from which thelow-boiling-point solvent was removed.
 14. The method for producing anelectrolyte solution according to claim 13, wherein thelow-boiling-point solvent is an alcohol.
 15. An electrochemical devicecomprising: an electrolyte solution, wherein the electrolyte solution isan electrolyte solution including a solvent formed from a sulfone and amagnesium salt dissolved in the solvent, or an electrolyte solutionincluding a solvent formed from a sulfone and a non-polar solvent, and amagnesium salt dissolved in the solvent.
 16. The electrochemical deviceaccording to claim 15, wherein the electrochemical device is amagnesium-using battery, capacitor, sensor, or magnesium ion filter. 17.The electrochemical device according to claim 16, wherein the battery isa secondary battery, an air battery, or a fuel cell.
 18. Theelectrochemical device according to claim 17, wherein the secondarybattery is a magnesium ion battery that has the electrolyte solution asan electrolyte layer.